Engine brakes or retarders are used to assist and supplement wheel brakes in slowing heavy vehicles, such as tractor-trailers. Engine brakes are desirable because they help alleviate wheel brake overheating. As vehicle design and technology have advanced, the hauling capacity of tractortrailers has increased, while at the same time rolling resistance and wind resistance have decreased. Thus, there is a need for advanced engine braking systems in today's heavy vehicles.
Problems with existing engine braking systems include high noise levels and a lack of smooth operation at some braking levels resulting from the use of less than all of the engine cylinders in a compression braking scheme. Also, existing systems are not readily adaptable to differing road and vehicle conditions. Still further, existing systems are complex and expensive.
Known engine compression brakes convert an internal combustion engine from a power generating unit into a power consuming air compressor.
U.S. Pat. No. 3,220,392 issued to Cummins on Nov. 30, 1965, discloses an engine braking system in which an exhaust valve located in a cylinder is opened when the piston in the cylinder nears the top dead center (TDC) position on the compression stroke. An actuator includes a master piston, driven by a cam and pushrod, which in turn drives a slave piston to open the exhaust valve during engine braking. The braking that can be accomplished by the Cummins device is limited because the timing and duration of the opening of the exhaust valve is dictated by the geometry of the cam which drives the master piston and hence these parameters cannot be independently controlled.
Engine brake actuators in electronically-controlled engine brake systems permit the independent control of the timing and duration of the opening of the exhaust valve. Examples of these include the engine brake systems disclosed in Pitzi U.S. Pat. No. 5,012,778; Faletti et al. U.S. Pat. No. 5,255,650; and Sickler U.S. Pat. No. 4,572,114.
Known engine brake actuators utilize low and high fluid pressure sources in coordination with an electronic control to open the exhaust valve for a selectable duration.
U.S. Pat. No. 4,464,977 issued to Brundage on Aug. 14, 1984, discloses a fluid pressure powered actuator having a control element in magnetic circuit with a solenoid coil wherein the control element comprises a sleeve disposed about and movable relative to a ported stem. The ported seem includes high and low pressure grooves in fluid communication with high and low fluid pressure sources, respectively, via a series of passages disposed within the ported stem. Both the high pressure groove and the low pressure groove are in partial fluid communication with a groove disposed in the control element. The control element groove in turn is in fluid communication with a control pressure chamber adjacent an operating member having two integral, axially adjacent pistons. Movement of the control element varies the communication between the grooves to change the fluid pressure in the control pressure chamber. The pistons are fastened to the ported stem such that movement of the pistons due to the change in fluid pressure in the control pressure chamber moves the ported stem relative to the control element.
U.S. Pat. No. 5,161,501 issued to Hu on Nov. 10, 1992, discloses a slave piston for use in an engine retarder. The slave piston is disposed in a slave piston cylinder contained in a housing and includes a longitudinal bore extending down from a top surface of the slave piston. A stationary valve member is disposed between a screw and a spring within the longitudinal bore. The valve member has an aperture disposed adjacent to a slot of the screw for placing a region of the slave piston cylinder above the slave piston in fluid communication with a region of the longitudinal bore below the valve member. The slave piston further includes a radial bore that connects the longitudinal bore to a circumferential groove disposed in an outer wall of the slave piston. The radial bore is initially covered by the valve member such that the radial bore is not in fluid communication with the longitudinal bore.
In operation, a high pressure fluid pulse is supplied to the cylinder region above the slave piston to thereby apply high pressure fluid to the top surface of the piston to move it in a downward direction. After sufficient slave piston displacement relative to the valve member, the radial bore is uncovered. The circumferential groove is in turn prearranged to align at this point with a passage disposed in the housing and connected to a low pressure fluid recovery area such that high pressure fluid in the region above the slave piston escapes to thereby clip the downward movement of the slave piston.